The invention relates to a vessel for the continuous treatment of molten metals under reduced pressure, according to the circulation process, especially for continuous degassing steel melts, this vessel being provided in its bottom, with an inlet pipe which dips into the molten metal, and an outlet pipe for the molten metal which has been treated, this outlet pipe being located so that it is spatially separated from the inlet pipe and, in particular, dipping into the molten metal.
Vessels of this type are employed, in particular, in the degassing of liquid steel according to the socalled "circulation process" (Ruhrstahl-Heraeus-process). In this process, the liquid steel, contained in a ladle which is positioned beneath the vessel, is lifted into the vessel by introducing conveying gas into the inlet pipe, and by applying suction to the vessel, and flows, in a continuous stream, through the outlet pipe of the vessel, and back into the ladle. In this process, the length of time for which the steel is treated is given by its circulation rate, which depends, in its turn, on the diameter of the vessel and on the cross-sections of the inlet and outlet pipes (German Offenlegungsschrift No. 1 458 874 U.S. Pat. No. 31 36 834).
Having regard to achieving as high a production rate as possible, and to avoiding heat losses during the treatment of liquid steel, the steelmaker endeavors to minimize the duration of the treatment to which the steel is subjected.
In the past, attempts have already been made to increase the circulation rate of the liquid steel by increasing the cross-sections of the inlet pipe and/or the outlet pipe of the vessel. However, for a given diameter of the vessel-bottom, the inlet pipe and/or the outlet pipe can be enlarged only by a limited amount. Since the flowing steel subjects the refractory lining of the vessel to an extremely powerful erosion effect, the inlet and outlet pipes require to be located, in the vessel-bottom, with an adequately large clearance, both with respect to each other, and in the directions of the vessel walls, in order to ensure that the refractory lining has a sufficiently long service life.
If, accordingly it is desired, on the grounds of metallurgical or economic considerations, to shorten the time for which the steel is treated, it was always necessary, in the past, to employ a degassing vessel with correspondingly increased dimensions.
The use of a suitably larger vessel not only requires the deployment of additional amounts of capital, but it is often absolutely impossible, for space-related reasons, to install a larger vessel in a plant which is already in existence.